nd fall into paralogisms, even on the
simplest matters of geometry, I, convinced that I was as open to error
as any other, rejected as false all the reasonings I had hitherto taken
for demonstrations; and finally, when I considered that the very same
thoughts (presentations) which we experience when awake may also be
experienced when we are asleep, while there is at that time not one of
them true, I supposed that all the objects (presentations) that had ever
entered into my mind when awake had in them no more truth than the
illusions of my dreams. But immediately upon this I observed that whilst
I thus wished to think that all was false, it was absolutely necessary
that I, who thus thought, should be somewhat; and as I observed that
this truth,--"_I think, hence I am,_"--was so certain and of such
evidence that no ground of doubt, however extravagant, could be alleged
by the skeptics capable of shaking it, I concluded that I might without
scruple accept it as the first principle of the philosophy of which I
was in search.

In the next place, I attentively examined what I was, and as I observed
that I could suppose that I had no body, and that there was no world nor
any place in which I might be; but that I could not therefore suppose
that I was not; and that on the contrary, from the very circumstance
that I thought to doubt of the truth of other things, it most clearly
and certainly followed that I was; while on the other hand, if I had
only ceased to think, although all the other objects which I had ever
imagined had been in reality existent, I would have had no reason to
believe that I existed; I thence concluded that I was a substance whose
whole essence or nature consists only in thinking, and which, that it
may exist, has need of no place, nor is dependent on any material thing;
so that "I"--that is to say, the mind by which I am what I am--is wholly
distinct from the body, and is even more easily known than the latter,
and is such that although the latter were not, it would still continue
to be all that it is.

After this I inquired in general into what is essential to the truth and
certainty of a proposition; for since I had discovered one which I knew
to be true, I thought that I must likewise be able to discover the
ground of this certitude. And as I observed that in the words "_I think,
hence I am,_" there is nothing at all which gives me assurance of their
truth beyond this, that I see very clearly that in